1. Field of the Invention
The invention relates to electrical connectors. More specifically, the invention relates to electrical connectors with strain relief features.
2. Brief Description of Earlier Developments
Various types of electrical connectors rely upon surface mount technology (SMT) to secure the connector""s contacts to an underlying substrate. SMT connectors provide numerous benefits over earlier connectors, such as simplified manufacturing and lower costs.
While providing such advantages, the use of SMT may raise other issues. One concern, for example, involves the ability of the solderjoint between the contact and the underlying substrate to absorb forces caused by, for example, shipping, handling, mating and thermal cycling. Should one solderjoint become unusable as a result of damage from any of these events, the entire connector adversely may be affected.
Ball grid array (BGA) technology is one type of SMT. Generally speaking, an electrical connector using a BGA has a housing with a contact therein. A fusible element, typically a solder ball, secures to each contact. The solder balls serve as the primary connection between the contact and the surface of the substrate. A reflow process fuses the solder ball to the substrate. During the reflow process, a beneficial xe2x80x9cself-centeringxe2x80x9d feature of BGA technology occurs. Specifically, as the solder reflows, the surface tension of the solder helps to align the connector properly with the conductive pads on the underlying substrate.
As with SMT connectors, forces on the solder joint in a BGA connector also poses a concern. Because of the self-centering ability of BGA connectors, however, many of the solutions used in SMT connectors cannot be used on BGA connectors. Therefore, a need exists to develop techniques for providing strain relief to BGA connectors.
The invention overcomes the above-mentioned limitations in the earlier developments and provides techniques for providing strain relief to BGA connectors. In particular, the invention provides a connector body with a retention post that may be inserted into a through hole in a printed circuit board (PCB). The post fits in the through hole without an interference fit. The post diverts some of the forces acting on the solder joint between the contacts and the PCB pads by allowing the connector body and the PCB to absorb some of the forces.
It is an object of the invention to provide an electrical connector with strain relief features.
It is a further object of the invention to provide a ball grid array electrical connector with strain relief features.
It is a further object of the invention to provide strain relief features to a ball grid array electrical connector compatible with the self-centering capability of the connector.
It is a further object of the invention to provide an electrical connector made with simplified manufacturing steps.
These and other objects of the invention are achieved in one aspect of the invention by an electrical connector mountable to a substrate. The electrical connector comprises a housing, a surface mount contact secured to the housing and adapted to surface mount to the substrate, and a non-surface mount hold down secured to the housing and adapted to mount to the substrate. The surface mount contact includes a fusible element, for example, a solder ball, a plurality of which may form a matrix array. The electrical connector is constructed such that it remains substantially parallel when mounted to the substrate. The electrical connector may further comprise a standoff secured to the housing. The standoff is adapted to retain the housing a distance from a surface of the substrate or to limit flattening of a solderjoint between the surface mount contact and the substrate. The standoff may be a part of the hold-down. The non-surface mount hold down of the electrical connector may be a post extending outwardly from the housing and is adapted to enter a hole in the substrate.
These and other objects of the invention are achieved in another aspect of the invention by a ball grid array connector mountable to a substrate. The ball grid array comprises a housing and a plurality of contacts within the housing. The ball grid array further comprises a plurality of fusible elements secured to the contacts for mounting the connector to the substrate, and a hold down adapted to enter the substrate. The hold down is secured to the housing. The ball grid array connector may further comprise a standoff extending from the housing and adapted to retain the housing a distance from a surface of the substrate or to limit flattening of the fusible elements during reflow. The standoff may be a part of the hold-down. The hold down may be a post extending outwardly from the housing. The fusible elements may be solder balls. Furthermore, the ball grid array connector may be constructed such that it remains substantially parallel when mounted to the substrate.
These and other objects of the invention are achieved in another aspect of the invention by a method of mounting an electrical connector to a substrate. The method comprises providing a substrate, and an electrical connector having a contact and a hold down. The electrical connector may be a ball grid array connector. The method further comprises securing the contact to the substrate, placing the hold down into the substrate, and securing the hold down to the substrate. The securing may comprise soldering the hold down to the substrate. The method may further comprise constructing the electrical connector such that it remains substantially parallel when mounted to the substrate. Also, the method may comprise balancing the electrical connector on the substrate such that the electrical connector remains substantially parallel to the substrate during the securing. Furthermore, the securing of the contact may occur before the securing of the hold down.
These and other objects of the invention are achieved in another aspect of the invention by a method of preventing the skewing of an electrical connector when being mounted to a substrate. The method comprises providing an electrical connector having a first part with a mass greater than a second part, and balancing the first and second parts of the electrical connector such that the electrical connector remains substantially parallel to the substrate when mounting to the substrate. The balancing may comprise removing material from the first part of the electrical connector and/or adding material to the second part of the electrical connector. The electrical connector may be a ball grid array connector.
These and other objects of the invention are achieved in another aspect of the invention by an electrical connector mountable to a substrate. The electrical connector comprises a housing having a mounting end facing the substrate, and a plurality of contacts secured to the housing. The electrical connector further comprises a plurality of fusible elements, each secured to a respective one of the plurality of contacts, and a standoff extending a distance from the mounting end of the housing. The standoff may allow partial flattening of the fusible elements. The distance may be selected so as to limit flattening of the fusible elements during reflow, or to prevent bridging between adjacent fusible elements. The fusible elements may be, for example, solder balls.
These and other objects of the invention are achieved in another aspect of the invention by an improved ball grid array connector mountable to a substrate. The improvement comprises a hold-down adapted to enter an opening in the substrate. The hold-down may be adapted to enter the opening without an interference fit.